Frequency and amplitude sound changer



Sept. 17, 1940. H. McCURDY 2,214,770

FREQUENCY AND AMPLITUDE "SOUND CHANGER Filed June 7, 1958 a ll Jzqarzzik 030% j 7 M 7 Patented Sept. 17, 1940 UNITED STATES PATENTOFFICE FREQUENCY AND AMPLITUDE SOUND CHANGER 5 Claims.

This invention is a frequency and amplitude sound wave changer and is animprovement in the type of apparatus set forth in my U. S. Patent No.2,113,055.

In that apparatus the incoming, cylindrical stream of gas, as theexhaust from a combustion motor, is divided into gradually decreasing,coaxial beams and these were each expanded, in its own relative portionof an elongate cylindrical chamber formed in advance of a transversecenter-perforate barrier, each arrested part of the streamperpendicularly impacting its barrier before its flow was arrested. Theabruptly stopped part of the stream was allowed to expand in an elongatespace between two opposite end barriers and then to pass radially toatmospheric air pressure through lateral ports in the apparatus. Whilethis greatly reduced the amplitude of exhaust waves these could besensed in some surrounding area in certain range around the muffler.

The present invention involves the same principle of expansion chambersand barriers but aims to so break up and expand the stream of gas as toobtain a higher degree of efficiency in destroying the amplitude of thesound waves.

An object is to provide means for intercepting the fractions (cylindric,concentric layers) of the wave forming stream just as the layerinitially enters its. relative breaker or expanding chamber; this beingotherwise unobstructed in any manner transversely or longitudinally sothat each shaved-off layer can expand as a tube in an expansion spaceor" much length existing between the shaving-off means and the nextfollowing reduction barrier. In other words the advancing, cylindriclayer of gas is first shaved off and. obliquely deflected and thenprogressively flows, as will be shown, to and along its expansionchamber, instead, as in the said patent device, of being sliced off anddirected straight radially and then substantially reversed in flow(toward the entrance) before its escape to the atmospheric ports.

Further, an object is to provide for the division of each concentriclayer of the gas stream into sub-divisions or layers, as may bedesirable in destroying high amplitude waves of sound incident to somestimuli.

Also, it is an object of the invention to provide for the elimination ofreversing moments in the gas stream flow and the undesired diffractionof the sound waves, to eliminate outlets radially of the axis of thestream, and to effect a generally or principally unidirectional flow thesliced-off,

expanding and expanded concentric, annular fractions of the parentstream or gas.

Additionally, an object of the invention is to provide a soundcontrolling device in which a parent stream is divided intosubstantially, transverse, equal concentric layers and for the expansionthereof in substantially equal volume chambers to avoid undesireddifferential reaction as between the several layers.

Carrying the invention further, an object is. to provide a mufileraffording a series of coaxial, axially elongate, concentric,progressively decreasing cross-area expansion chambers which arecommonly open, that is without radial obstruction, for the effectivelength of their gas expanding portions, to the axis of a path of gasflow and which chambers are each longitudinally unobstructed except fora relatively shallow, transverse, conoidal annulus concentric to theaxis, and the chambers in echelon relation on the axis and allpreferably opening to atmosphere in one (axial) direction.

And further, an object is to provide means for negating as far asdesired diffraction of the sound waves in reverse as to the line or pathof axial discharge from the device as by the provision of suitabletransverse louvers of circular form.

The invention consists of certain advancements in this art as set forthin the ensuing disclosure and having, with the above, additional objectsand advantages, as hereinafter developed, and whose construction,combinations and details of means, and the manner of operation will bemade manifest in the description of the herewith illustrativeembodiment; it being understood that modifications, variations andadaptations may be resorted to within the scope, spirit and principlesof the invention as it is more directly claimed hereinbelow.

Figure l is an axial section of the silencer.

Figure 2; is a transverse section on line 22 of Fig. 1.

Figures 3 and 4 are detail views of a sinuous edged bafile.

In this adaptation of the Wave changer to an internal combustion motor,the exhaust gases therefrom are received in a conduit 2 which is fixedconcentrically in a rearwardly flared first end wall 3' of a first stagechamber or cylinder 3 of a diameter of greater dimension than that ofthe conduit 2 at its connection with the end wall 3' which is providedwith a central intake opening 3 of substantially the size of the bore ofthe exhaust pipe or conduit 2.

The chamber 3 in this disclosure extends rearwardly of and is inconcentric spaced relation to the contiguous intruded end of a secondexpansion chamber 5 having a front end wall 4 provided with a concentricround opening 4' which is of suitably less diameter than the firstintake opening 3" in wall 3 of chamber 3. This stage wall 4 ispreferably in the form of a conoidal annulus and its obliquity isrearward or with the axial gas. path of flow, and presents anappreciable frontal area 4 across the projected bore at the intakeopening 3"; this is clearly depicted in Fig. 1. It will be noticed thatthere is no obstacle between the axis of the chamber 3 and its innersurface for the length of that part of the chamber between walls 3 and 4excepting for means positioned near the front wall 3 and which has thefunction of checking back and slicing off the outermost annular layer ofthe exhaust stream incoming at the opening 3. This first-stage slicingmeans may include one or more, here two, slightly axially spaced,rearwardly pitched, conoidal annuli 3 and 3 the forwardmost of which hasa flow hole somewhat smaller than the intake opening 3' and the latterof which, 3, has a flow hole of the same size as that, 4', leading tothe second stage expansion chamber 5.

Thus the first cutting ring 3 takes or slices off a concentric outermostlayer of the incoming stream and deflects it obliquely outwardly andrearwardly. This feature of the invention permits the sliced off layerof gas under pressiu'e to freely expand in that space between wall 4 andthe ring 3 and radially between the stream of gas flowing through thesecond ring 3 (and moving as a core toward the equi-size hole 3' in thewall 4) and the chamber wall 5.

This is a wholly different expanding function than was possible in theform of device of said patent where the gas had first to be stopped bythe equivalent wall 4 to be sliced off, whence it was expanded by areversal of flow toward the front end. In the present invention the gasis sliced off and expands as. it flows un directionally with the mainstream toward the far, dis charge end of the silencer.

The far end of the second stage chamber 5 is in spaced, concentricrelation with. a suitably smaller, third expansion chamber '5 having arearwardly pitched, conoidal, front end wall 6 with a central opening 6materially smaller than the opening 4 of the second stage so as topresent a substantial abutment area. G or closure for its end of thechamber 5 to permit a reduced core of the stream of gas to flow intochamber '5 for expansion. However, as inthe case of chamber 3, thechamber 5 has near the forward wall 4 a slicing oiT means in the form ofa plurality of slightly axially spaced, conoidal rings 5 and 5 thefirst, 5 of which is provided with a central hole somewhat smaller thanthe hole 4' but larger than the hole of its associate ring 5 which, inturn, is about equal to the hole ii in wall 6. The core of the streampassing the hole in the secondary slicing ring 5 flows on to and entersthe chamber 7 by way of the wall hole 8 but that layer of the streamwhich is intercepted by the slicing rings 5 and 5 is directed obliquelyrearwardly toward the cylinder wall 6 to be freely expanded in the spacetherein concentrically about the fast flowing central core of the gasstream moving toward the wall 63. The effective expansion chamber spacein section 5 is unobstructed in any way except for the slicing off means5 -5 The core stream passing through the wall opening 6' is sliced justback of the wall 6 by a rearwardly pitched, conoidal ring l to bedirected obliquely rearwardly for expansion in the space concentricallysurrounding the final small stream core of gas permitted to flow pastthe opening in the ring l The far end of the chamber 1 is concentricallyspaced about a closed filler or body 9.

From the above it will be seen that the expanded gas flows from chamber3 by way of an annular outlet port 3r; that from chamber 5 flows from anannular exhaust port 5x, and that from chamber 1 from an annular exhaustport ix; with all of the spent gases moving in a common, unidirectional,axial stream. It is understood that while this is the preferred exhaustprinciple, lateral outlets may be employed if so desired in any or allof the chambers in combination or not with the axial direction exhaustports.

The width or radial dimension of the several slicing off rings, fromtheir bore hole to their rims is preferably of such a degree as to besteffect the slicing operation and permit, then, the least barrier to theflow of the layer of the stream over the rim of the ring into therearward, relative expansion space.

There is shown in Figs. 3 and 4, a modification of the form of slicingelement as comprising a conoidal annulus 10 having a plurality of symmetrical, angular-1y spaced fins or blades H with radial edges !2 andarcuate edges i3 from the tips of the fins to the roots of the radialedges in order around the annulus so as to provide flow openings, withinthe circle enscribing the tips of the fins, to effect the flow of theinterrupted layer of gas in streams of differential rate of speed, orrelative starting time, toward the expansion chamber in rear of therelative annulus H] to best utilize the expanding capacity of thechamber by smoothing out the stream instead of tending to choke thestream by diverting the full layer into the chamber at one instant. Ifand when preferred, the fins H may be given a common helical pitch ashere indicated to helically swirl the expanding gases.

A narrow, annular, inwardly projecting, rearwardly inclined soundarresting ring It may be fixed in the outlet end of each of theexpansion chambers, as indicated in Fig. 3.

Because of the reduced diameters of the several expansion chambers35-'i, the exhaust end of each may be provided with suitable number andsize of circular louvers !6. Or the difference in area can be equalizedby proportioning the chamber diameters to give the desired size ofvents. While the louvers it are shown as of conoidal form, it isunderstood that their shape and angle may be varied to suit. Also thelength of the chambers may be varied to give equal or unequal volumes ofexpansion for fluids and to vary or equalize the time lags between thesubdivisions of the exhaust stream.

The sinuous edges of the exhaust baffle Ill constitute a means to causethe sound wave to be gradually diffused. In Fig. l the end of onechamber of the apparatus is shown as having an end edge in the form ofone full pitch of a helix H, with the result that the exhaust stream andsound wave passing over this sinuous edge is gradually retarded in itsdischarge to the atmosphere in a circle around the terminal.

What is claimed is:

l. A sound wave changer having an annular, exhaust conduit member havingan opening Whose edge is a concentric helix and the axial width of theopening being substantially a full pitch of the helix around the axis ofthe member; said helical discharge edge operating to efiect the gradual,processional diffusion of a wave body in a helical, radial form tolesser outer pressure space and said edge preventing higher amplitudeportion of the wave from passing at one instant in any material angulardegree in one transverse plane.

2. A sound wave changer having an annular, open end exhaust member whosedischarge end edge is a helix over which a stimulated fluid wave isprocessionally dissipated while passing out of the open end of themember,

37 A sound wave changer including a discharge member having a flowopening to its bore and the edge of which includes a helix and theopening having an axial length about equal to one pitch of the helix andoperative to prevent diffusion to any material amount in any transverseplane of the opening.

4. A sound wave change-r including an exhaust tube whose outlet end fsin the form of a concentric helix along its edge; whereby to causedissipation of discharging fluid only as an infinite number of axiallyisolated pencils radial to the helical edge of the outlet from the tube.

5. An exhaust tube whose wall terminates progressively along its lengthin the form of a helix of substantially one full pitch and the ends ofthe helix being joined by a substantially longitudinal edge part of thetube.

HOWARD MoCURDY.

